The transmission of digital information and data between systems has become an essential part of commonly used systems. With such systems, information content is transmitted and received in digital form as opposed to analog form. Information long associated with analog transmission techniques, for example, television, telephone, music, and other forms of audio and video, are now being transmitted and received in digital form. The digital form of the information allows signal processing techniques not practical with analog signals. In most applications, the user has no perception of the digital nature of the information being received.
Many digital communication devices (particularly wireless digital telephones) suffer some amount of signal degradation during the transmission from the originating device to the receiving device. This degradation often results in the loss of some information, some distortion in the signal, or some noticeable noise in the received signal (e.g., as in the case of a wireless telephone). Generally, the more frequent the errors, the more significant the loss of information at the receiving device, which consequently leads to more objectionable performance of the communications system.
To correct this problem, the electronics industry has adopted various error correction techniques which counteract the effects of signal degradation and improve or ensure the integrity of the information at the receiving device. Hence, many digital communications systems available on the market use error correction methods that are each able to accomplish reasonable communication quality under normal operating conditions.
Typically, error correction techniques function by including additional amounts of "redundant" information in the signal transmission from the originating device. This redundant information is often referred to as error correction code. The redundant information is used to check the validity of the information as received at the receiving device. For example, parity checking, check summing, cyclic redundancy checking, forward error correction coding, are several of the more widely used, well known error correction methods. These error correction methods help ensure the integrity of the received information, thereby ensuring the proper and error free operation of any applications being run on top of the received information, such as, for example, a wireless modem link supporting a remote network node.
The problem with the above error correction methods is that they reduce the available bandwidth of the signal transmission. With most digital communication systems, there is a very finite amount of spectrum allocated to the transmission channel. The transmission of redundant error correction code decreases the amount of bandwidth in the channel available for the transmission of the "real" information. When transmission conditions are bad, such as for example, during a thunderstorm or during periods of solar interference, the error correction methods are required for nominal operation. However, under good transmission conditions, error correction is not needed and available bandwidth is wasted transmitting error correction codes.
The unnecessary transmission of redundant information harms system efficiency. The wasted transmission of error correction codes is very undesirable where the bandwidth of the communications channel is very limited, as in digital wireless communication systems in high population density areas (e.g., cities). In addition to wasting bandwidth, unnecessary error correction wastes processor capacity in the receiving and transmitting devices. Signal processing effort is wasted encoding and decoding the error correction information, which in turn, needlessly slows the performance of the system and increases power consumption.
However, using current technology, error correction is still required in order to ensure the communications system will still function when signal transmission conditions are not good. Accordingly, the power and the amount of error correction used is typically chosen such that the communications system or the application being served by the communications system will run satisfactorily under average operating conditions. If a greater degree of reliability is required, the error correction used is chosen in view of worst case operating conditions.
These error correction methods are static in that they are typically chosen during the design process of the communications system. A static error correction method is chosen and designed into a communications system in accordance with the typical expected operating conditions of the system. Static error correction is, in this manner, a design compromise based upon the expected use of the system.
Thus, static assignment makes inefficient use of spectrum in case of good transmission conditions, or yields an unacceptable bit error rate under bad conditions. This is undesirable for wireless systems that are designed for and used to serve high population density. Very powerful error correction methods are available, but they involve more processor power than may actually be required under the circumstances, resulting in excess power consumption in the device. The additional signal processing also leads to increased transmission delay time.
Static assignment presents a special problem in the case of DECT/PHS/PCS/GSM and other wireless telecom systems operating under time-variant transmission conditions. The transmission conditions of the communications channel differ depending upon the time the communications system is being used. Consequently, the error correction method chosen for implementation is usually not the most efficient for any one particular circumstance. This forces trade offs and causes engineers to design for the worst case conditions. This also leads to wasted bandwidth.
Thus, what is needed is a method which tailors the error correction technique to the transmission conditions. What is required is a method which dynamically selects the type of error correction required depending upon the circumstances of the communications channel. What is required is a method which adjusts error correction according to the observed quality of the Flexibly adapting the error detection/correction method according to the observed signal transmission quality. In addition, the required solution should reduce the signal processing load needed for error correction as transmission conditions allow. The present invention provides a novel solution to the above requirements.